Research On Phase Compensation Methods In Comb-Based Large Capacity Coherent Optical Communication Systems

With the rapid development of emerging services such as artificial intelligence,big data,and the Internet of Things,global data traffic is increasing rapidly,making people put forward higher requirements for the transmission capacity and communication rate of optical networks.Wavelength division multiplexing(WDM)coherent optical communication is the key technology for realizing large-capacity communication in the current optical fiber communication system.In traditional WDM coherent optical communication systems,multiple independent lasers are used to provide carriers of different wavelengths,which makes the system cost continue to rise as the number of channels increases,and the DSP cost at the receivers will also increase.Replacing the independent lasers with frequency comb as the WDM light sources can reduce the system cost,and use its phase coherence to reduce the computational complexity of DSP and reduce the power consumption of the receivers.It is expected to be applied in future large-capacity coherent optical communication systems.However,the dispersion and nonlinear effects in the transmission will weaken the phase coherence.At present,several phase compensation methods using the phase coherence of optical combs are mainly suitable for medium and short-distance transmission systems.They cannot achieve low-complexity phase compensation in comb-based long-haul large capacity coherent optical communication systems.In this paper,aiming at the comb-based large capacity coherent optical communication systems,how to improve system performance and achieve low-complexity phase compensation under long-haul transmission conditions is studied.The specific research contents are as follows:1.The weakening of phase coherence caused by dispersion in optical comb-based coherent optical communication systems is investigated.Based on the characteristic that the phase coherence weakening of adjacent channels is smaller,an innovative parameter passing master-slave carrier phase recovery algorithm is proposed to achieve low complexity phase compensation.By changing the master-slave parameter passing structure and the slave phase tracker algorithm,the algorithm eliminates the residual phase noise of the slave channel caused by the weakening of phase coherence,thus realizing low-complexity phase compensation for all channels.The simulation results show that,under the condition of long-haul transmission,the phase compensation performance of proposed algorithm is significantly better than the two existing master-slave algorithms,and the performance is the same as ICPR,but its computational complexity is only 7.1%of ICPR,so the amount of calculation is large reduce.2.The weakening of phase coherence caused by both nonlinear effects and dispersion in optical comb-based coherent optical communication systems,which affects signal quality,is investigated.From the essential causes of this phenomenon,a master-slave phase compensation method using optical phase conjugation(OPC)is proposed,which realizes low-complexity phase compensation while effectively reducing the bit error rate and improving system performance.This phase compensation method introduces the OPC module into the comb-based communication systems and places it in the middle of the link,so that the transmission time delay of each channel is consistent.It solves the problem of phase coherence weakening caused by dispersion from the hardware system and mitigates nonlinear damage.Simulation results show that the computational complexity of this method is consistent with MS-CPR,but its average bit error rate(BER)is only 9.3%of MS-CPR and 60%of ICPR.To sum up,this paper deeply studies the phase compensation methods in the comb-based large capacity coherent optical communication systems.Aiming at the problem of phase coherence weakening caused by dispersion and nonlinearity,a parameter passing master-slave carrier phase recovery algorithm and the master-slave carrier phase recovery method using OPC are proposed,and the effectiveness of the proposed method is verified by simulation.The research results of this paper provide a feasible solution for low-complexity phase compensation in comb-based large capacity communication systems,and are of great significance for promoting the application of optical combs in long-haul large capacity communication systems.